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Is there any risk of shock from attaching or detaching wires to a 9V battery?

Discussion in 'General Electronics Discussion' started by novicefedora, Jun 27, 2020.

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  1. novicefedora

    novicefedora

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    Jun 25, 2020
    Is there any risk of shock from attaching or detaching wires to a 9V battery? When I'm cutting wires soldered to the battery and PCB or attaching or soldering one wire at a time?
     
  2. Alec_t

    Alec_t

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    Jul 7, 2015
    No, unless the battery is connected to a large inductive load. That will generate a high back-emf when its current is interrupted; high enough to give a nasty jolt but unlikely enough to kill you (unless you have a pacemaker or heart-condition).
     
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  3. novicefedora

    novicefedora

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    Jun 25, 2020
    I'm opening a bug zapper, and I got a shock when my fingers accidentally touched something internal, could be the PCB. It has a battery without labels, from the size I guessed it would be a 9V battery. I don't know the power of the high voltage converter it has.

    I'll be disconnecting the racquet net connected to the output capacitor, in it's place there will be a copper coil, there will be a spark gap behind one of the the output capacitor connections and one end of a copper coil, the other end of the output capacitor will be attached directly to the other end of the copper coil. Can this copper coil act as an large inductive load.
     
  4. Alec_t

    Alec_t

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    A bug zapper includes an inductor for stepping the voltage from the battery up to a very high voltage which may well be rectified and held on a capacitor. That could be enough to give you a nasty schock. The same arrangement is used in a camera's electronic flash. The camera manual would normally contain a warning message about the danger.
    Yes.
     
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  5. novicefedora

    novicefedora

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    Jun 25, 2020
    Then how would I disconnect, reconnect and solder wires with an inductor? All the videos on YouTube show people cutting wires without feeling shock, how are they doing it?
     
  6. Alec_t

    Alec_t

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    You switch off the device and make sure that any capacitor in the device has time to discharge. This may take a second or so if the circuit has been designed properly to include a discharge path, or may take a lot longer in a cheapo circuit with no such intended path.
     
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  7. novicefedora

    novicefedora

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    Jun 25, 2020
    The bug zapper I have has wires soldered to the battery and PCB, and the shock I got earlier, I turned it off and removed it. Will turning it off and pressing the zap button discharge the capacitor? Can I check this with line tester or multimeter?
     
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    Depends how the circuit has been designed.
    Only if you have a meter rated to handle the very high voltage.
     
  9. novicefedora

    novicefedora

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    Jun 25, 2020
    Do you mean standalone camera flash attached to DSLRs or the ones found in disposable cameras? Will a standalone camera flash give me more control over the duration of the EMP pulse, like making it last for only 1ms, should this be enough to disable low current circuitry?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Not another silly EMP thread!
     
  11. Alec_t

    Alec_t

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    Both.
    The flash duration in a camera flash unit (other than a disposable camera) is usually adjustable by the microcontroller in the camera or standalone flash.
     
  12. novicefedora

    novicefedora

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    Jun 25, 2020
    Where are other silly EMP threads?
     
  13. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    In our "twilight zone" section. Should you so wish I can easily move this thread over there.
     
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  14. novicefedora

    novicefedora

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    Jun 25, 2020
    Why? Will this thread get more replies there? Is that a threat?

    I think the main point of this thread is to find out if there is any risk of electric shock when detaching, attaching wires, which are connected to batteries, PCBs with high voltage converters, capacitors. EMP is secondary.
     
  15. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Definitely not as it is not possible to reply in that section.
    An offer.
    Simply avoid terms that sound like woo woo science.

    There definitely is if there are high voltage parts that are charged,
    The reasons for this can be manifold:
    - high battery voltage (yes, batteries of electric vehicles can have more than 100 V)
    - generated high voltages (as in electronic flashes, vacuum tube operated devices etc.)

    The general procedure is to deactivate the device, disconnect the battery (assuming it is of the standard low voltage type this is an easy task) and wait for any charges to be discharged. In a good design so called bleeding resistors will discharge high voltage components within a few seconds or minutes. In a less well designed circuit lacking bleeder resistors the discharge can take very long. It may be aided by manually connecting a bleeder resistor across suspect components (e.g. capacitors).
    Without further knowledge of the circuit in question no more detailed advice can be given.
     
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  16. novicefedora

    novicefedora

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    Jun 25, 2020
    Here are two photos of front and back of the PCB:

    Back: Red and Blue wires are from battery, other two red wires under from the plug.
    [​IMG]

    Front: The large capacitor at the top is 2000V, the smaller one is 400V
    [​IMG]

    After using and turning off, if I were to touch it while removing the covers, I'm getting a shock. I think I managed to discharge the capacitor with the shock, so now I'm using a line tester to discharge the capacitor when I open it, one end of the capacitor gives off a spark when I touch it with a line tester.

    I'm using 1 square millimeter normal electricity copper wire to make a coil, one end is soldered near left end of the capacitor, the other end is a spark gap at the other end of the capacitor but it is unable to create EMP to effect any digital device, at the most it can cause a line which lasts for fraction of a second on the screen of a mobile phone.

    And what are woo woo words?
     
    Last edited: Jul 2, 2020
  17. Alec_t

    Alec_t

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    Jul 7, 2015
    So your zapper is fed with AC voltage which probably gets rectified to drive an oscillator. The oscillation gets stepped up by the transformer then rectified and stored on the 2000V cap. If there is a bleed resistor across that cap, it's not evident from the pic. Methinks the cap would hold a possibly lethal charge for a considerable time.
     
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  18. novicefedora

    novicefedora

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    Jun 25, 2020
    Thanks for your valuable analysis. If a bleed resistor is something which is attached to the bottom of the capacitor, then there is no bleed resistor. If not, I'll have to take a photo from the other angle.

    What could I be doing wrong, have I not wound the coil tight enough or the wire has higher Ohms, the most it could do when I turn it on is cause thin lines on the mobile phone's screen for a fraction of a second. I used an enamel wire after this, and it couldn't cause any EMP effect too. Will this be enough to affect for up to 2.5 inches? If I need to increase the power, do I need to add higher capacitor or build my PCB circuit?
     
  19. Martaine2005

    Martaine2005

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    May 12, 2015
    You need ten turns on the coil. You can avoid a shock by placing tin foil on your head and covering your ears. Only then you can touch the capacitor terminals. If it hurts to touch it, try not to do it again.

    Martin
     
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  20. davenn

    davenn Moderator

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    Sep 5, 2009
    thread closed
    It's getting screwball
     
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